1. Field of the Invention
The invention relates to the use of an aqueous polyurethane dispersion adhesive for producing biodisintegratable composite foils. The invention also relates to a process for producing the composite foils and to the composite foils produced by the process.
Flexible packaging is often composed of composite foils adhesive-bonded to one another by a suitable adhesive, where at least one of the foils bonded to one another is a polymer foil. There is high demand for degradable composite-foil packaging, where the term degradable materials is also understood to include materials that decompose under biological conditions, i.e. disintegrating or compostable materials.
The major challenge consists in providing materials which have the necessary functionality and stability but which when subject to stimulation from a bioactive environment, are degraded or decomposed with maximum rapidity and to maximum extent. The trigger for the degradation process can be microbiological, hydrolytic, or oxidative degradation at a specific site within the main chain of a polymer. All of the degradation products should exhibit maximum safety and minimum toxicity and not be capable of accumulation within the natural environment, and this means that they should be subject to complete and final microbial degradation. The adhesive used for the adhesive-bonding of the foils also has an effect on biodisintegratability. The adhesive is intended firstly to provide a stable adhesive bond but secondly also to promote degradability, i.e. disintegration of the foil composite. It is extremely difficult to achieve simultaneous compliance with, and optimization of, these fundamentally contradictory requirements.
2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98
WO 96/35733 discloses degradable and compostable moldings inclusive of sheet-like structures. They are produced by using aqueous dispersions of polyurethanes having urea groups. The polyurethanes are composed of a diisocyanate component, a diol component, a diamine component in the form of diaminosulfonates, and optionally hydrophilic polyether alcohols.